Isostatic die, particularly for ceramic tiles and relative method

Abstract: The isostatic die for pressing items, in particular ceramic tiles, makes for greater uniformity of pressing by compensating for differences of density occurring when loading the matrix with the powders to be pressed; said die consists of an elastic membrane (5), delimiting externally a cavity in the punch or in the matrix, the membrane being connected to elements (1; 3; 18; 103a; 111; 128; 129; 208; 316) for controlling deformation, among which is a plate (18; 111) attached in a predetermined way to the membrane (5) and/or to the cavity of the matrix and/or of the punch; its use is foreseen in establishments for the manufacture of ceramic items.

Description: The invention concerns die means, suitable for isostatic moulding ceramic tiles, according to the preamble of claim 1. IT-A-1104511, by the same applicant relates to a method and a device for achieving uniform pressing of ceramic tiles. The method envisages the application to the free surface of the clay mixture introduced into the opening of the die, during the action of pressing of an elastic moulding surface, or elastic membrane, held in firm contact with the clay mixture, to form one face of the tile, by means of an incompressible fluid: this, to neutralize the effects of zones of disuniform density in the body of the formed tile which would cause uneven shrinkage on firing, with consequent variations in the size, or linearity, of the sides of the tile and/or of the planarity of its surface and with the additional possibility of cracking or breakage. The methods and the device according to that particular prior art document have introduced the fundamental concept of an incompressible fluid, for example, oil, acting on an elastic membrane and interposed between the punch and the membrane. However, said method and device do not always enable sufficiently flat (back) surfaces, and hence sufficiently uniform tile thickness, to be readily achieved, particularly in the case of large formats: We are aware of a die, featuring an auxiliary punch base with, on its front face, a chessboard-like array of large flat squares surrounded by channels for the distribution of the liquid, communicating with the internal surface of the overlying membrane by means of large, corresponding square alveoli, forming part of an intermediate punch-plate superimposed on said auxiliary punch base. The smooth inner surface of the overlying (vulcanized) membrane is moulded to afford an array of large, flat square protruding bosses surrounded by channels corresponding exactly to the aforesaid configuration of the upper face of said base of auxiliary punch. However this punch is of extremely complex construction; furthermore, the considerable size of the square alveoli causes a notable deformation of the membrane with consequent unacceptable defects of planarity in the pressed tile. This type of mould is also described as forming part of the prior art in IT-U-MI93000071, Fig. 1 and in IT-A-MI92002158, page 3. EP-A-0556163, which is per se an intermediate document but concerns the same type of mould, discloses a mould having a plurality of cavities defined by a lattice to which a membrane is anchored; however the lattice cannot be provided with a membrane obtained by vulcanized elastomeric substance, such as rubber or resin, since, when the liquid elastomeric substance is poured on the lattice, the cavities become completely filled with the elastomeric substance and no room is therefore available for the incompressible fluid. IT-U-214739 discloses a punch for uniform pressing of ceramic tiles, comprising a plurality of cavities among which a lattice is inherenty defined, said cavities containing an incompressible fluid, i. e. oil, and being closed on the side facing the clay mixture to be pressed by means of an elastic membrane, the elastic membrane comprising a central zone and a peripheral zone, those parts of the membrane not covering the cavities being anchored to the body of said punch at respective peripheral and intermediate anchoring zones, each cavity being intermediately occupied by a respective piston and serving as a guide for allowing axial movements of the piston inwardly and outwardly with respect to the cavity. Each piston is further externally provided with a seal for the incompressible fluid peripherally engaged with the internal surface of the respective cavity in order to prevent oil from coming into contact with the membrane. In that mould, however, the pistons deteriorate the corresponding edges of the membrane when they move into the cavities to compensate disuniform density of the clay mixture. Furthermore, when the membrane has to be formed, particularly by vulcanization, the pistons have to be inserted into the cavities before the liquid elastomeric membrane is poured to coat the face of the punch: therefore a difficulty arises in that the pistons cannot be located at precise axial positions inside the cavity, being it essential, for proper functioning, that each piston be located at intermediate sections of the respective cavity, so that they can be moved outwardly, under the pression of the oil, and also inwardly, under the pression of the clay mixture. Correct positioning of the pistons is also essential in order to avoid excessive variations of thickness of the membrane. IT-U-214739 is considered as being the closest prior art. IT-A-MI92002158, filed on 18/09/1992, which is a prior national right in Italy, additionally discloses elastic planar caps in said cavities. Therefore, a separate set of claims is formulated for Italy. Such prior art may be subject to further improvements with a view to eliminating the said drawbacks. The technical problem is therefore to find a die of the aforesaid type which is easy to manufacture, by providing it with a vulcanised membrane, and in which the membrane is not subjected to deterioration by the action of any movable part inserted into the cavities. The invention solves the above-mentioned technical problem by adopting die means, suitable for isostatic moulding ceramic tiles, comprising two dies (punch and matrix), at least one die having a plurality of cavities containing an incompressible fluid, said cavities being closed on the side facing the clay mixture to be pressed by means of an elastic membrane, the elastic membrane comprising a central zone and a peripheral zone, those parts of the membrane not covering the cavities being anchored to the body of the said semi-die at respective peripheral and intermediate anchoring zones, each cavity being occupied, at an enlarged portion thereof, by a respective intermediate controlling element for controlling the deformation of the membrane interposed between the incompressible fluid and the membrane, characterized in that said intermediate element is elastically deformable under the action of said incompressible fluid, or of the membrane, and said enlarged portion serving as a seat for said intermediate element. This allows a greater protection of the membrane by the action of the incompressible fluid, since the latter can act on the membrane by the interposition of flexible elements. Some embodiments of the invention are illustrated, by way of example, in the four sheets of drawing, in which: Figure 1 is the plan view, partially sectioned, of a punch whose top surface has alveoli for the introduction of, the oil, each alveolus having a cap made of preformed elastic material, on the upper side made rough and covered in an adhesive substance, with covering elastic membrane vulcanized in situ, reproducing, on the external face, the negative of the back of the tile; Figure 2 is the partial and partially sectioned elevation of a punch as in Figure 4 during the vulcanization of the elastic membrane over the preformed caps: purely by way of example, the first alveolus on the left being occluded by a plate cap whereas the second being occluded by a hollow cap; Figure 3 is a perspective view of a plate cap; Figure 4 is a perspective view of a hollow cap; Figure 5 is a partial elevation of a punch with alveoli respectively for a plate cap and a hollow cap; Figure 6 is a section of part of a punch with membrane and hollow cap for each alveolus. The Figures show: 117 (Figure 1), the top, flat surface of punch P, having frame 118; 119, the lowered plane of an alveolus with underlying tapered cavity 120 with liquid inlet hole 121; 122, a hollow cap joining with rim 123 of the alveolus; 124, grooves that surround the raised sections 125 of the membrane 126 that shape the back of the tile during pressing; 127 (on the left of Figure 2) the supporting surface of the bottom face of the elastic pre-pressed plate cap 128; 129, the top face of the elastic pre-pressed hollow cap, having peripheral rim 130; 131, (Figure 6) longitudinal oil, or liquid in general, inlet channels, communicating with transverse channels 132; 133, the intermediate anchorage zones of membrane 126, achieved with the application of a suitable substance; 134 peripheral anchorage zones; 8, the moulding matrix of the elastic membrane 126. The edges of the elastic plate 128 and the external face of rim 130 of the hollow cap can be anchored to rim 123 of the corresponding alveolus: in the first case the liquid being prevented from coming into contact with the anchoring zones 133 and 134. If, on the other hand, the cap is not anchored along the rim, it becomes easier for the membrane 126 to move as the cap is floating. The join with the top face of each cap 129, 130 is obtained during vulcanization phase of the membrane 126. The invention as described is susceptible to numerous changes and variations all included in the scope of the present invention as defined by the claims. Furthermore, all the details of execution may be replaced by others that are technically equivalent. In practice the materials employed, as well as the forms and dimensions, can be varied as required without departing from the giuridical domain of the following claims.

Claims: Claims for the following Contracting States : AT, BE, CH, LI, DE, DK, ES, FR, GB, GR, LU, MC, NL, PT, SE, IE Die means, suitable for isostatic moulding ceramic tiles, comprising two dies, punch and matrix, at least one die (P) having a plurality of cavities (119, 120, 121, 127) containing an incompressible fluid, said cavities being closed on the side facing the clay mixture to be pressed by means of an elastic membrane (124, 125, 126), the elastic membrane (124, 125, 126) comprising a central zone and a peripheral zone (118), those parts of the membrane (124, 125, 126) not covering the cavities (119, 120, 121, 127) being anchored to the body of the said die (P) at respective peripheral and intermediate anchoring zones, each cavity (119, 120, 121, 127) being occupied, at an enlarged portion (119; 127) thereof, by a respective intermediate controlling element (128; 129) for controlling the deformation of the membrane (124, 125, 126) interposed between the incompressible fluid and the membrane (124, 125, 126), characterized in that, said intermediate element (128; 129) is elastically deformable under the action of said incompressible fluid, or of the membrane (124, 125, 126), and said enlarged portion (119; 127) serve as a seat for said intermediate element (128; 129). Die means as claimed in claim 1, wherein said intermediate element has the shape of an hollow cap (129) having an hollow part facing the respective cavity (119, 120, 121) and in direct contact with the incompressible fluid. Die means as claimed in claim 1, wherein said intermediate element has the shape of a plate cap (128). Die means as claimed in any one of the preceding claims, wherein said intermediate element (128; 129) has an outer face substantially co-planar with the portions of the body of the punch (P) to which the membrane (124, 125, 126) is anchored. Die means as claimed in any one the preceding claims, wherein said membrane (124, 125, 126) is anchored to said intermediate element (128; 129). Claims for the following Contracting State : IT Die means, suitable for isostatic moulding ceramic tiles, comprising two dies, punch and matrix, at least one die (P) having a plurality of cavities (119, 120, 121, 127) containing an incompressible fluid, said cavities being closed on the side facing the clay mixture to be pressed by means of an elastic membrane (124, 125, 126), the elastic membrane (124, 125, 126) comprising a central zone and a peripheral zone (118), those parts of the membrane (124, 125, 126) not covering the cavities (119, 120, 121, 127) being anchored to the body of the said die (P) at respective peripheral and intermediate anchoring zones, each cavity (119, 120, 121, 127) being occupied, at an enlarged portion (119; 127) thereof, by a respective intermediate controlling element (129) for controlling the deformation of the membrane (124, 125, 126) interposed between the incompressible fluid and the membrane (124, 125, 126), said intermediate element (129) being elastically deformable under the action of said incompressible fluid, or of the membrane (124, 125, 126), said enlarged portion (119; 127) serving as a seat for said intermediate element (129), characterised in that said intermediate element has the shape of an hollow cap (129) having an hollow part facing the respective cavity (119, 120, 121) and in direct contact with the incompressible fluid. Die means as claimed in claim 1, wherein said intermediate element (129) has an outer face substantially co-planar with the portions of the body of the punch (P) to which the membrane (124, 125, 126) is anchored. Die means as claimed in any one of the preceding claims, wherein said membrane (124, 125, 126) is anchored to said intermediate element (129).

Inventors: ALGERI MARIS, ANNOVI NUNZIO, ALGERI, MARIS, ANNOVI, NUNZIO
Applicants: ALGERI MARIS, ALGERI, MARIS
Application year: 1994
Main classification: B28B3
IPC codes: B28B3, B30B11, B30B5